In addition to cleaning, laundry detergent compositions desirably have other benefits. One is the ability to confer soil release properties to fabrics, particularly those woven from polyester fibres. These fabrics are mostly co-polymers of ethylene glycol and terephthalic acid, and are sold under a number of tradenames, e.g. Dacron, Fortrel, Kodel and Blue C Polyester. The hydrophobic character of polyester fabrics makes their laundering difficult, particularly as regards oily soil and oily stains. The oily soil or stain preferentially "wets" the fabric. As a result, the oily soil or stain is difficult to remove in an aqueous laundering process.
High molecular weight (e.g., 40,000 to 50,000 M.W.) polyesters containing random ethylene terephthalate/polyethylene glycol terephthalate units have been used as soil release compounds in laundry detergent compositions--see for example U.S. Pat. Nos. 3,962,152 and 3,959,230. During the laundering operation, these soil release polyesters adsorb onto the surface of fabrics immersed in the wash solution. The adsorbed polyester then forms a hydrophilic film which remains on the fabric after it is removed from the wash solution and dried. This film can be renewed by subsequent washing of the fabric with a detergent composition containing the soil release polyesters.
A major disadvantage of the known detergent formulations, however, is that they can adversely effect cleaning performance in other areas of laundry detergency, especially clay soil detergency. Presumably this is the result of the polymer depositing on soil which is already adhered to the fabric surface, thereby preventing solubilization or dispersion of the soil by other components of the detergent composition.
It is also known that introducing specific quaternary ammonium surfactants into the aqueous laundry liquor can provide increased deposition of terephthalate-based soil-release polymers and hence provide superior removal of oily soils and stains (see U.S. Pat. No. 4132680).
Quaternary ammonium surfactants are themselves known to have a detrimental effect on clay soil detergency and anti-redepositon and, if anything, therefore adding a quaternary ammonium surfactant merely compounds the problem.
It has now been discovered that certain terephthalate soil release polymers having a specified ratio of ethyleneoxy terephthalate to polyethyleneoxy terephthalate units and specified molecular weight and preferably having polyethyleneglycol terminating groups at both ends of the polymer chain provide excellent soil-release performance in a detergency context without detriment to clay soil detergency and anti-redeposition. Indeed in a low or zero phosphate detergent compositions, clay soil cleaning performance is actually enhanced. Furthermore, incorporation of a water-soluble quaternary ammonium surfactant promotes further increases in polymer deposition and improved soil-release performance again surprisingly without detriment to clay-soil detergency. Moreover, the quaternary ammonium surfactant is beneficial from the viewpoint of promoting soil-release performance in the presence of anionic surfactant components.